1. Field of the Invention
The present invention relates to image forming apparatus and system for exchanging data between a copying machine and an attachment device thereof.
2. Description of the Prior Art
In a copying machine which is intended to improve a operability and finely control a quality of copy, a data transfer apparatus for exchanging various data (for example, data indicating copy enable and sorter enable) between the copying machine and an attachment device having a sorter and an input sensor is usually required. As shown in FIG. 1, in a prior art data transfer apparatus of this type, a copy machine 11 has a central processing unit (CPU) 12, an I/O controller 13, an output driver 14, an input interface 15, a CPU power supply circuit 16 and an attachment device power supply circuit 17, and mainly controls key entry and display. An attachment device 18 has a sequence controller 19, an input interface 20A, an output driver 21A, an output load 22A and an input sensor 23A, and controls a copy sequence and a sorter sequence. A flat cable, for example, having a number of lines determined depending on the number of various signals is used to transfer the data between the copying machine 11 and the attachment machine 18.
The input interface 15 of the copying machine 11 and the input interface 20A of the attachment device 18 may use photo-couplers as shown in FIG. 2 in order to suppress noises.
In any case, however, as the number of types of signals to be transferred increases, the number of pins of a connector increases. As a result, costs of the connector and the cable increase and the reliability of the apparatus is degraded.
The applicant of the present invention has proposed an apparatus for serially transferring data among CPU's in a copying machine having a plurality of CPU's. However, the proposed apparatus uses, in addition to an exclusive data line, a clock line for synchronizing the CPU's and a protocol line for communicating transfer enable of the CPU's. As a result, the number of lines increases.
Also, it is inconvenient because of a fixed master and slave relation.